A method of heat treating a drill bit

Abstract

The present application relates to a kind of drill bit heat treatment method, belong to heat treatment technical field.To solve the problem of high cost and poor quality of existing product core, provide a kind of drill bit heat treatment method, the method includes carburizing treatment, the carburizing treatment includes strong penetration treatment: the anchor drill made of 20CrMnTi material is placed into carburizing furnace, control temperature is at 900 ℃ ~ 940 ℃ is carried out strong penetration treatment, after strong penetration treatment, keep temperature at 900 ℃ ~ 940 ℃ under the condition of early diffusion treatment is carried out;Again cooling to 850 ℃ ~ 870 ℃ is carried out late diffusion treatment, late diffusion carbon potential control is at 0.6 ~ 0.7;After ending, first time out of antechamber slow cooling to 280 ℃ ~ 320 ℃, then into heating chamber and is heated to 850 ℃ ~ 890 ℃ and carries out heat preservation treatment, carbon potential control is at 0.5 ~ 0.6, after ending, second time out of antechamber slow cooling to 280 ℃ ~ 320 ℃, then out of furnace cooling.The present application has excellent surface hardness performance and core performance.

Description

Technical Field

[0001] The invention relates to a heat treatment method for a drill bit, belonging to the technical field of heat treatment. Background Art

[0002] Heat treatment refers to the processing of solid metal or alloy materials by heating, heat preservation and cooling to obtain the expected structure and performance. At present, carburizing is generally used to improve the surface wear resistance and strength of steel. The processed parts are placed in a carburizing agent, heated to the mid-phase austenite temperature, and heat-insulated to allow carbon atoms to penetrate into the surface layer of the parts. The purpose is to increase the carbon content of the surface layer of the parts to make them have high strength and wear resistance, while the working core still maintains the toughness and plasticity of low-carbon steel. The carburizing process generally includes a strong carburizing stage and a diffusion stage. The processing time of the strong carburizing stage of the existing carburizing treatment is longer than the diffusion time, which is not conducive to the gradient distribution of carbon concentration in steel parts and has a greater impact on their hardness and strength.

[0003] Drill bits, made of steel, are widely used in blasting projects in mines, ports, roads, tunnels, and other construction projects, such as breaking rock and drilling holes. These tools include down-the-hole drill bits, hydraulic threaded drill bits, and mining ball-tooth drill bits. To improve their strength and hardness, they undergo the aforementioned carburizing treatment, followed by subsequent heat treatments such as quenching and tempering. However, the existing heat treatment process adopts a slow cooling after the diffusion stage, which is not conducive to the overall refinement of the material's organizational structure, resulting in poor grain structure and poor strength of the product. The different control of carbon potential in different stages will also affect the performance of the core. The hardness of the core is relatively low. At the same time, the organizational transformation of the core is not sufficient, the grain size is relatively coarse, the grain boundaries are more obvious, and brittle fracture is prone to occur during use. In addition, most existing drilling tool materials are expensive, which is not conducive to industrial production. For example, a heat treatment method for 23CrNi3Mo disclosed in patent document (publication number: CN103305668B) is as follows: the untreated material is placed in a carburizing furnace for heating, carburizing treatment is carried out at a temperature of 890°C to 960°C, and then high-temperature tempering is carried out at a constant temperature of 580°C to 720°C for 3 to 5 hours, and then cooled, quenched, and then low-temperature tempered to obtain the corresponding heat-treated product. The materials used are relatively expensive, which is not conducive to industrial production. Currently, there are no drilling products using 20CrMnTi materials. It is necessary to develop a new heat treatment technology that can ensure the performance indicators of the product core. Summary of the Invention

[0004] In view of the above defects in the prior art, the present invention provides a heat treatment method for a drill bit, which solves the problem of how to improve the strength of the drill bit and the hardness of the core.

[0005] The object of the present invention is achieved through the following technical solution: a heat treatment method for a drill bit, the method including carburizing treatment, characterized in that the carburizing treatment includes the following steps:

[0006] A. Carburizing treatment: Place the drill bit made of 20CrMnTi material into the carburizing furnace and perform carburizing treatment at a temperature of 900℃~940℃. The carburizing potential is controlled at 1.0~1.2.

[0007] B. Diffusion treatment: After the strong infiltration treatment is completed, the temperature is maintained at 900℃~940℃ for early diffusion treatment, and the early diffusion carbon potential is controlled at 0.7~0.8; then the temperature is lowered to 850℃~870℃ for late diffusion treatment, and the late diffusion carbon potential is controlled at 0.6~0.7; after the end, the steel is slowly cooled to 280℃~320℃ out of the antechamber for the first time, and then enters the heating chamber to heat up to 850℃~890℃ for insulation treatment, and the carbon potential is controlled at 0.5~0.6. After the end, the steel is slowly cooled to 280℃~320℃ out of the antechamber for the second time, and then taken out of the furnace for cooling.

[0008] By using a drill bit made of 20CrMnTi material and controlling the carbon potential at a higher level during the intensive carburizing stage, the carbon concentration in the early stage is high, so that intensive carburizing is carried out at 900℃~940℃, which can achieve rapid carburizing; then the diffusion stage is specifically divided into the early and late stages, and the diffusion temperature and carbon potential in the late stage are lower than the conditions of the early diffusion stage, which can prevent surface cracks from occurring during the diffusion stage and prevent grain boundary cracks from occurring in the internal grain structure; more importantly, after the diffusion stage is completed, after the first slow cooling out of the antechamber, it is reheated to 850℃~890℃ for treatment, and the carbon potential is controlled at 0.5~0.6, and then two slow cooling out of the antechamber are carried out, the purpose of which is to change the core structure of the drill bit, change the grain size, and make the grains more effectively refined, which is equivalent to the improvement of the secondary austenite structure, so as to have a finer grain structure, so that the outer layer of the drill bit has a better carburized layer, achieving the high surface hardness requirement, and also making the core have better hardness performance, while ensuring the performance of the core. Performance testing of the resulting product revealed the advantages of high surface hardness, with the core also exhibiting good hardness indicators. The surface structure fully met the requirements, the core structure was fully transformed, the grain size was fine, and brittle fracture did not occur during use. The surface hardness performance index (HRC) reached above 55, and the core hardness performance index (HRC) reached above 41. Furthermore, by employing the above-described method of the present invention, it is possible to manufacture drill bits using the relatively low-cost 20CrMnTi material, thereby achieving the advantage of cost reduction. The above-described drill bits can be down-the-hole drill bits, hydraulic threaded drill bits, mining ball-tooth drill bits, rock drill bits, and the like.

[0009] In the above-mentioned drill bit heat treatment method, the duration of the carburizing treatment in step A is preferably 2.5 to 3.0 hours. By maintaining a higher carbon potential during the initial carburizing stage, the duration of the carburizing stage is shortened relative to the diffusion stage, unlike the conventional method of extending the carburizing stage. This is achieved by combining the 20CrMnTi material used to enhance the effectiveness of carburizing, ensure a higher hardness index for the surface layer, and further improve the quality requirements of the core.

[0010] In the above-mentioned heat treatment method for a drill bit, preferably, the initial diffusion treatment in step B lasts for 3.0 to 4.0 hours, and the final diffusion treatment lasts for 30 to 45 minutes. The purpose of lengthening the initial diffusion stage compared to the final treatment is to allow for better diffusion under the relatively high carbon potential conditions of the initial stage, and to allow for a relatively short diffusion period under the relatively low carbon potential conditions of the final stage. This allows for better diffusion of carbon atoms within the structure, further effectively preventing grain boundary cracks and improving overall quality.

[0011] In the above-mentioned drill bit heat treatment method, the holding treatment in step B preferably lasts for 2.5 to 3 hours, and the first and second slow cooling periods out of the antechamber are each independently 40 to 50 minutes. The purpose of performing these two slow cooling periods is to further strengthen and refine the grain structure, thereby improving the quality of subsequent products and laying the foundation for subsequent quality, particularly by enhancing the quality requirements of the core.

[0012] In the above-mentioned heat treatment method for a drill bit, preferably, the carburizing step B further includes the following steps:

[0013] C. Tempering treatment: Tempering the drill bit after the treatment in step B under the protection of inert gas and controlling the temperature at 450℃~500℃;

[0014] D. Quenching and tempering treatment: After the tempering treatment is completed, the temperature is raised to 850℃~900℃ for quenching and tempering treatment, and the carbon potential is controlled at 0.3~0.4. After the end, cool down;

[0015] E. Then perform isothermal quenching and tempering to obtain the corresponding heat-treated drill bit.

[0016] This is equivalent to performing subsequent tempering, quenching and tempering treatments after the carburizing stage, which can be more conducive to ensuring the strength performance of the drill bit, making the surface layer have good hardness performance, and the core also has relatively excellent performance. Specifically, by first performing tempering treatment under inert gas protection after step B of the carburizing stage, it can play a role in preventing oxidation, and the tempering treatment is performed to better remove stress, which is conducive to balancing the organizational structure, so as to have better strength performance and ensure the performance of the core. Then, in the quenching and tempering stage, the temperature is raised to 850℃~900℃ for quenching and tempering treatment, and the carbon potential is controlled at 0.3~0.4, which can also better play a protective role, prevent surface oxidation or decarburization, more fully realize the metallographic structure of ferrite to martensite transformation, and improve the organizational structure; finally, austempering and tempering treatment are performed, which more effectively form bainite structure, and after tempering treatment, the organizational structure can be stabilized, internal stress is eliminated, and the product's excellent surface hardness performance and core performance are effectively achieved.

[0017] In the above-mentioned drill bit heat treatment method, the quenching and tempering treatment in step D preferably lasts for 3.0 to 4.0 hours. After the quenching and tempering treatment, the product is oil-cooled for 15 to 20 minutes, then de-oiled for another 10 to 20 minutes, and then removed from the furnace for cooling. The oil cooling treatment can better obtain a martensitic or bainitic microstructure. The subsequent de-oiling treatment is to automatically drip away oil stains attached to the product surface, reducing quenching oil waste and easing the burden of subsequent cleaning. Furthermore, after cooling out of the furnace, the temperature can be raised to 580°C to 600°C for tempering for 2.5 to 3.0 hours.

[0018] In the above-mentioned heat treatment method for the drill bit, preferably, the austempering treatment and tempering treatment in step E are specifically as follows:

[0019] The temperature is raised to 850℃~900℃ for austempering treatment, and the carbon potential is controlled at 0.3~0.4. After the end, the temperature is controlled at a salt bath temperature of 190℃~220℃ for heat preservation treatment. After the end, the salt is removed, and the temperature is controlled at 160℃~200℃ for tempering treatment after removal from the furnace. It is air-cooled to room temperature to obtain a heat-treated drill bit. Further salt bath treatment is mainly performed to make the tissue transformation more complete, so that the ferrite, pearlite and cementite of the raw material structure are rapidly cooled by the cooling medium to a process from the martensite or bainite transformation point to the transformation end point, so that the tissue is fully transformed, the structure is more effectively improved, and the performance of the product after heat treatment is improved. As a further preferred embodiment, the austempering treatment time is 3.0~4.0 hours, and the tempering treatment time is 3.0~3.5 hours. More preferably, the holding time at the salt bath temperature can be further set to 15~30 minutes, and the salt removal time can be set to 10~15 minutes.

[0020] In the above-mentioned heat treatment method for the drill bit, preferably, the carburizing agent used in the strong carburizing treatment and diffusion treatment in step A and step B is propane, and the diluent is methanol or ethanol.

[0021] In summary, the present invention has the following advantages compared with the prior art:

[0022] 1. Through the above-mentioned strong infiltration treatment and diffusion treatment, and the improvement of the secondary slow cooling treatment after the diffusion treatment, the advantage of high surface hardness can be effectively achieved, and the core also has a good hardness index. The surface organization fully meets the requirements, the core organization is fully converted, the grain size is small, and brittle fracture will not occur during use.

[0023] 2. The present invention performs subsequent tempering, quenching and tempering after carburizing, which is more conducive to ensuring the strength performance of the drill bit, making the surface layer have good hardness performance and the core also have relatively excellent performance. It can better play a protective role, prevent surface oxidation or decarburization, more fully realize the metallographic structure of ferrite to martensite transformation, and improve the microstructure. Finally, austempering and tempering are performed to more effectively form bainite structure. After tempering, the microstructure can be stabilized and internal stress can be eliminated, effectively achieving the product with excellent surface hardness performance and core performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a metallographic analysis diagram of the surface layer of the drill bit after heat treatment according to Example 1 of the present invention.

[0025] Figure 2 This is a metallographic analysis diagram of the core of the drill bit after heat treatment according to Example 1 of the present invention.

[0026] Figure 3 This is a metallographic analysis diagram of the surface layer of the drill bit after heat treatment in Comparative Example 1 of the present invention.

[0027] Figure 4 This is a metallographic analysis diagram of the core of the drill bit after heat treatment in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0028] The technical solution of the present invention will be further specifically described below through specific embodiments and drawings, but the present invention is not limited to these embodiments.

[0029] Example 1

[0030] A heat treatment method for a down-the-hole drill bit includes a carburizing treatment, wherein the carburizing treatment includes a strong carburizing treatment and a diffusion treatment, specifically:

[0031] A down-the-hole drill bit made of 20CrMnTi material can be a down-the-hole drill bit that has been pre-processed by CNC. The down-the-hole drill bit is placed in a carburizing furnace, heated to 920°C and controlled at 920°C for a strong carburizing and heat preservation treatment for 3 hours. The strong carburizing potential is controlled at 1.0. The carburizing agent can be propane and the diluent can be methanol.

[0032] After the strong infiltration treatment is completed, the temperature is maintained at 920℃ for early diffusion treatment for 3.5 hours, but the early diffusion carbon potential is adjusted and controlled at 0.75; after the time is up, the temperature is lowered to 860℃ for late diffusion treatment for 30 minutes, the carbon potential is adjusted, and the late diffusion carbon potential is controlled at 0.65; after the end, the first time of slow cooling out of the front room for 45 minutes is carried out to reduce the temperature to about 300℃, and then enter the heating chamber to heat up to 875℃ for insulation treatment for 2.5 hours, during which the carbon potential is controlled at 0.6. After the end, the second time of slow cooling out of the front room for 45 minutes is carried out to about 300℃, and then the furnace is taken out of the furnace and air-cooled to room temperature.

[0033] After the carburizing treatment B, the following specific steps are also included:

[0034] The down-the-hole drill bit is tempered for 3.5 hours under the protection of inert gas nitrogen and controlled at 480° C. The tempering treatment under the protection of inert gas is beneficial to prevent the surface oxidation of the drill bit;

[0035] After the tempering treatment is completed, the temperature is raised to 860℃ for quenching and tempering and heat preservation treatment for 3.5 hours, and the carbon potential is controlled at 0.4. After the end, it is cooled in the oil tank for 20 minutes and then drained for 15 minutes. It is then air-cooled for 10 minutes and cleaned. After the cleaning is completed, it is dried at 120℃ and then tempered at 600℃ for 3 hours before entering the next process directly.

[0036] The temperature is raised to 880℃ and kept for 3.5 hours, and the carbon potential is controlled at 0.4. After the end, it is taken out of the furnace and kept at a salt bath temperature of 200℃ for 20 minutes, and salted for 10 minutes. It is immediately tempered at 180℃ for 3 hours after being taken out of the furnace, and then taken out of the furnace and air-cooled to room temperature. The residual salt and impurities on the surface of the product are cleaned to obtain the corresponding heat-treated drill bit.

[0037] The obtained down-the-hole drill bit was subjected to metallographic analysis. Figure 1 (Metallic analysis of surface tissue, 500 times) and Figure 2 (Metal analysis of core structure, 500 times) Figure 1 and Figure 2 The analysis of the microstructure shows that: the surface structure is fine needle-shaped martensite level 1 + 8% lower bainite + retained austenite level 1 + carbide level 1; the core structure is low carbon martensite strip + bainite + ferrite level 1;

[0038] Three tests showed that the surface hardness HRC of the product was 55.7, 55.4 and 55.6 respectively; the core hardness HRC was 42.3, 42.1 and 41.9 respectively.

[0039] This shows that the surface structure fully meets the requirements, the core structure is fully transformed, the grain size is fine, and the performance is high.

[0040] Example 2

[0041] A heat treatment method for a down-the-hole drill bit includes a carburizing treatment, wherein the carburizing treatment includes a strong carburizing treatment and a diffusion treatment, specifically:

[0042] The down-the-hole drill bit made of 20CrMnTi material can be a down-the-hole drill bit that has been pre-processed by CNC. The down-the-hole drill bit is placed in a carburizing furnace, heated to 900°C and controlled at 900°C for a strong carburizing and heat preservation treatment for 3 hours. The strong carburizing potential is controlled at 1.15. The carburizing agent can be propane and the diluent can be methanol.

[0043] After the strong infiltration treatment is completed, the temperature is maintained at 900℃ for early diffusion treatment for 4 hours, but the early diffusion carbon potential is adjusted and controlled at 0.8; after the time is up, the temperature is lowered to 850℃ for late diffusion treatment for 45 minutes, the carbon potential is adjusted, and the late diffusion carbon potential is controlled at 0.6; after the end, the first slow cooling is carried out from the front room for 50 minutes to reduce the temperature to about 300℃, and then the temperature is raised to 890℃ in the heating chamber for insulation treatment for 3 hours, during which the carbon potential is controlled at 0.5. After the end, the second slow cooling is carried out from the front room for 50 minutes to about 300℃, and then the furnace is taken out and air-cooled to room temperature.

[0044] After the carburizing treatment B, the following specific steps are also included:

[0045] The down-the-hole drill bit is tempered for 3 hours under the protection of inert gas nitrogen and controlled at 450° C. The tempering treatment under the protection of inert gas is beneficial to prevent the surface oxidation of the drill bit;

[0046] After the tempering treatment, the temperature is raised to 870℃ for quenching and tempering for 3 hours, and the carbon potential is controlled at 0.3. After the end, it is cooled in the oil tank for 30 minutes, the oil is removed for 10 minutes, and then air-cooled for 15 minutes after leaving the furnace. After cleaning, the water vapor is dried at 120℃, and then tempered at 620℃ for 3.5 hours, and then directly enters the next process;

[0047] The temperature is raised to 850℃ for 3 hours, the carbon potential is controlled at 0.3, after the end, the furnace is discharged at 200℃ salt bath temperature for 20 minutes, the salt is 15 minutes, the furnace is discharged immediately at 160℃ tempering treatment for 3 hours, then the furnace is discharged and air cooled to room temperature, the product surface residual salt and impurities are cleaned, and the corresponding heat treated drill bit is obtained.

[0048] The obtained down-the-hole drill is subjected to metallographic structure analysis, and the results show that the properties of the surface layer structure and the core structure can reach the level equivalent to the metallographic analysis diagram of the corresponding surface layer structure and core structure in Example 1.

[0049] Three tests show that the surface hardness of the product is HRC 55.1, 55.3, 55.3 respectively, and the core hardness is HRC 41.6, 41.8, 41.9 respectively.

[0050] It is shown that the surface layer structure fully meets the requirements, the core structure conversion is sufficient, the grain size is small, and the use performance is high.

[0051] Example 3

[0052] A heat treatment method of a down-the-hole drill, the method comprising carburizing treatment, the carburizing treatment comprising strong carburizing treatment and diffusion treatment, specifically:

[0053] The down-the-hole drill made of 20CrMnTi material can make the down-the-hole drill which has been pre-processed by numerical control machining, the down-the-hole drill is placed in a carburizing furnace, the temperature is raised to 940℃ and controlled at 940℃ for strong carburizing heat preservation treatment for 2.5 hours, the strong carburizing carbon potential is controlled at 1.2, the carburizing agent can use propane, and the diluent can use methanol;

[0054] After the strong carburizing treatment is completed, the temperature is kept at 940℃ for 4 hours for early stage diffusion treatment, but the early stage diffusion carbon potential is adjusted and controlled at 0.7; after the time, the temperature is lowered to 870℃ for later stage diffusion treatment for 45 minutes, the carbon potential is adjusted and the later stage diffusion carbon potential is controlled at 0.7; after the end, the first time of out of the pre-chamber slow cooling is carried out for 40 minutes to reduce the temperature to about 320℃, then the heating chamber is entered to raise the temperature to 880℃ for heat preservation treatment for 3.0 hours, during which the carbon potential is controlled at 0.5, after the end, the second time of out of the pre-chamber slow cooling is carried out for 40 minutes to about 300℃, and then the furnace is discharged and air cooled to room temperature.

[0055] The above carburizing treatment B further comprises the following specific steps:

[0056] The discharged down-the-hole drill is tempered at 450℃ under the protection of inert gas nitrogen for 3.0 hours, which is beneficial to prevent the oxidation of the surface of the drill under the protection of inert gas;

[0057] After the tempering treatment is completed, the temperature is raised to 900℃ for quenching and tempering heat preservation treatment for 3 hours, and the carbon potential is controlled at 0.3. After the end, it is cooled in the oil tank for 20 minutes and the oil is removed for 15 minutes. It is then air-cooled for 10 minutes and cleaned. After the cleaning is completed, the water vapor is dried at 120℃, and then tempered at 580℃ for 3.5 hours before entering the next process directly.

[0058] The temperature is raised to 900℃ and kept for 3 hours, and the carbon potential is controlled at 0.35. After the end, it is taken out of the furnace and kept at a salt bath temperature of 200℃ for 20 minutes, and salted for 10 minutes. It is immediately tempered at 160℃ for 3.5 hours after being taken out of the furnace, and then taken out of the furnace and air-cooled to room temperature. The residual salt and impurities on the surface of the product are cleaned to obtain the corresponding heat-treated drill bit.

[0059] The metallographic analysis of the obtained down-the-hole drill bit showed that the performance of the surface structure and the core structure could reach the same level as the metallographic analysis diagrams of the corresponding surface structure and core structure in Example 1.

[0060] Three tests showed that the surface hardness HRC of the product was 56.3, 56.8 and 56.2 respectively; the core hardness HRC was 43.1, 42.9 and 43.2 respectively.

[0061] This shows that the surface structure fully meets the requirements, the core structure is fully transformed, the grain size is fine, and the performance is high.

[0062] Example 4

[0063] A heat treatment method for a down-the-hole drill bit includes a carburizing treatment, wherein the carburizing treatment includes a strong carburizing treatment and a diffusion treatment, specifically:

[0064] The down-the-hole drill bit made of 20CrMnTi material can be made into a down-the-hole drill bit that has been pre-processed by CNC. The down-the-hole drill bit is placed in a carburizing furnace, heated to 920°C and controlled at 920°C for a strong carburizing and heat preservation treatment for 3.5 hours. The strong carburizing potential is controlled at 1.15. The carburizing agent can be propane and the diluent can be methanol.

[0065] After the strong infiltration treatment is completed, the temperature is maintained at 920℃ for early diffusion treatment for 3 hours, but the early diffusion carbon potential is adjusted and controlled at 0.8; after the time is up, the temperature is lowered to 860℃ for late diffusion treatment for 30 minutes, the carbon potential is adjusted, and the late diffusion carbon potential is controlled at 0.65; after the end, the first time of slow cooling out of the front room for 40 minutes is carried out to reduce the temperature to about 310℃, and then enter the heating chamber to heat up to 850℃ for insulation treatment for 3.5 hours, during which the carbon potential is controlled at 0.6. After the end, the second time of slow cooling out of the front room for 40 minutes is carried out to about 310℃, and then the furnace is taken out of the furnace and air-cooled to room temperature.

[0066] After the carburizing treatment B, the following specific steps are also included:

[0067] The down-the-hole drill bit is tempered for 3.0 hours under the protection of inert gas nitrogen and controlled at 450° C. The tempering treatment under the protection of inert gas is beneficial to prevent the surface oxidation of the drill bit;

[0068] After the tempering treatment, the temperature is raised to 860℃ for quenching and tempering for 3.5 hours, and the carbon potential is controlled at 0.4. After the end, it is cooled in the oil tank for 20 minutes and then drained for 15 minutes. It is then air-cooled for 10 minutes and cleaned. After cleaning, it is dried at 120℃ and then tempered at 560℃ for 3 hours before entering the next process.

[0069] The temperature is raised to 870℃ and kept for 3 hours, and the carbon potential is controlled at 0.35. After the end, it is taken out of the furnace and kept at a salt bath temperature of 200℃ for 20 minutes, and salted for 10 minutes. It is immediately tempered at 190℃ for 3 hours after being taken out of the furnace, and then taken out of the furnace and air-cooled to room temperature. The residual salt and impurities on the surface of the product are cleaned to obtain the corresponding heat-treated drill bit.

[0070] The metallographic analysis of the obtained down-the-hole drill bit showed that the performance of the surface structure and the core structure could reach the same level as the metallographic analysis diagrams of the corresponding surface structure and core structure in Example 1.

[0071] Three tests showed that the surface hardness HRC of the product was 55.8, 55.4, and 55.2 respectively, and the core hardness HRC was 42.5, 42.6, and 43.1 respectively.

[0072] This shows that the surface structure fully meets the requirements, the core structure is fully transformed, the grain size is fine, and the performance is high.

[0073] Comparative Example 1

[0074] A heat treatment method for a down-the-hole drill bit includes a carburizing treatment, wherein the carburizing treatment includes a strong carburizing treatment and a diffusion treatment, specifically:

[0075] The down-the-hole drill bit made of 20CrMnTi material can be made into a down-the-hole drill bit that has been pre-processed by CNC. The down-the-hole drill bit is placed in a carburizing furnace, heated to 920℃ and kept warm for 3.5 hours. The strong carburizing potential requirement is 1.15. The carburizing agent can be propane and the diluent can be methanol.

[0076] Then, the diffusion temperature is maintained at 920℃ for 3 hours, and the carbon potential is required to be 0.8. Then, the temperature is lowered to the late diffusion temperature of 860℃ and maintained for 30 minutes, and the diffusion carbon potential is 0.65. After completion, it is taken out of the front chamber and oil-cooled in the oil tank for 20 minutes, then oil-dried for 15 minutes, and then air-cooled for 5 minutes before cleaning. Then the temperature is controlled to rise to 190℃ and maintained for 6 hours. After completion, it is taken out of the furnace and air-cooled to room temperature.

[0077] The obtained down-the-hole drill bit was subjected to metallographic structure analysis (500 times), combined with Figure 3 (Surface microstructure metallographic diagram, 500 times) and Figure 4 (Core structure metallographic diagram, 500 times) as shown: Figure 1 and Figure 2 The analysis of the organization shows that Figure 3 The corresponding surface structure is acicular martensite level 2 + retained austenite level 2 + carbide level 1, Figure 4 The corresponding core structure is low carbon martensite plate + martensite lath + ferrite level 3.

[0078] Three tests showed that the surface hardness HRC was 59.7, 60.3, and 60.2 respectively; the core hardness HRC was 38.2, 38.6, and 38.3 respectively.

[0079] The surface structure can also fully meet the requirements, but the hardness of the core structure is slightly low. In addition, as shown in the figure, the core structure transformation is not sufficient, the grain size is coarse, the grain boundaries are obvious, and brittle fracture is prone to occur during use.

[0080] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Persons skilled in the art may make various modifications, additions, or substitutions to the described embodiments without departing from the spirit of the present invention or exceeding the scope of the appended claims.

[0081] Although the present invention has been described in detail and certain specific embodiments have been cited, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.

Claims

1. A heat treatment method for a drill bit, the method comprising carburizing treatment, characterized in that: The carburizing treatment comprises the following steps: A. Carburizing treatment: Place the drill bit made of 20CrMnTi material into the carburizing furnace and control the temperature at 900℃~940℃ for carburizing treatment. The carburizing potential is controlled at 1.0~1.

2. B. Diffusion treatment: After the strong infiltration treatment is completed, the temperature is maintained at 900℃~940℃ for early diffusion treatment, and the early diffusion carbon potential is controlled at 0.7~0.8; then the temperature is lowered to 850℃~870℃ for late diffusion treatment, and the late diffusion carbon potential is controlled at 0.6~0.7; after the end, the steel is slowly cooled to 280℃~320℃ out of the antechamber for the first time, and then enters the heating chamber and heats up to 850℃~890℃ for insulation treatment, and the carbon potential is controlled at 0.5~0.

6. After the end, the steel is slowly cooled to 280℃~320℃ out of the antechamber for the second time, and then cooled out of the furnace; the time for the first slow cooling out of the antechamber and the second slow cooling out of the antechamber is independently 40~50 minutes.

2. The heat treatment method for a drill bit according to claim 1, characterized in that: The duration of the strong osmosis treatment in step A is 2.5 to 3.0 hours.

3. The heat treatment method for a drill bit according to claim 2, characterized in that: The time for the early diffusion treatment in step B is 3.0 to 4.0 hours, and the time for the late diffusion treatment is 30 to 45 minutes.

4. The heat treatment method for a drill bit according to claim 3, characterized in that: The heat preservation treatment time in step B is 2.5 to 3.0 hours.

5. The heat treatment method for a drill bit according to any one of claims 1 to 4, characterized in that: The carburizing step B also includes the following steps: C. Tempering treatment: Tempering the drill bit after the treatment in step B under the protection of inert gas and controlling the temperature at 450℃~500℃; D. Quenching and tempering treatment: After the tempering treatment is completed, the temperature is raised to 850℃~900℃ for quenching and tempering treatment, and the carbon potential is controlled at 0.3~0.

4. After the end, cool down; E. Then perform isothermal quenching and tempering to obtain the corresponding heat-treated drill bit.

6. The heat treatment method for a drill bit according to claim 5, characterized in that: The time of the quenching and tempering treatment in step D is 3.0 to 4.0 hours. After the quenching and tempering treatment, the product is oil-cooled for 15 to 20 minutes, and then de-oiled for 10 to 15 minutes before being taken out of the furnace and cooled.

7. The heat treatment method for a drill bit according to claim 5, characterized in that: The austempering and tempering treatments in step E are specifically as follows: The temperature is raised to 850℃~900℃ for isothermal quenching treatment, and the carbon potential is controlled at 0.3~0.

4. After the end, the drill is taken out of the furnace and the temperature is controlled at a salt bath temperature of 190℃~220℃ for insulation treatment. After the end, the salt is removed and the temperature is controlled at 160℃~200℃ for tempering treatment after taking out of the furnace. It is air-cooled to room temperature to obtain the heat-treated drill bit.

8. The heat treatment method for a drill bit according to claim 7, characterized in that: The time for the austempering treatment in step E is 3.0 to 4.0 hours; the time for the tempering treatment in step E is 3.0 to 3.5 hours.

9. The heat treatment method for a drill bit according to claim 7, characterized in that: The time of heat preservation treatment at the salt bath temperature is 15 to 30 minutes, and the time of salt bath treatment is 10 to 15 minutes.

10. The heat treatment method for a drill bit according to any one of claims 1 to 4, characterized in that: The carburizing agent used in the strong carburizing treatment and diffusion treatment in step A and step B is propane, and the diluent is methanol or ethanol.

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